1. Field of the Invention
The present invention is related to chip that has power-up strapping functionality and that can temporarily change a state or mode of the chip.
2. Background Art
Products are manufactured that include chips having a plurality of selectable functions. The selectable functions use devices that can perform different functions allows the chips to be used in a variety of different systems. In order to properly set the function of the device, a mode or state is usually selected for the device based on the product it is incorporated within. The mode or state can be selected using a strapping system (e.g., mode or state setting system) in a variety of ways, including using: a dedicated pin, a register control block controlled by software running in the product, or the like. Thus, because a designer knows what product is being made, when the chip is inserted into the product a function of the device can be set using a signal that designates a mode or state. Using a strapping system may be favored because it does not require using a dedicated pin. Pins are in limited supply on a chip, and avoiding having to use one to set a mode of the device is desired.
In an example strapping system, an input/output (I/O) device on the chip is controlled through an enable signal. When the output is not enabled, the input floats. When the input floats, the input can be coupled to a resistive element to provide a strapping signal. The resistive element can be pulled-up (i.e., producing a HIGH strapping signal) or pulled-down (i.e., producing a LOW strapping signal). The strapping signal can be stored in a latch device or a flip-flop. During a reset operation, the latch can store the strapping signal. After the reset operation, the latch can close and the strapping signal can be substantially permanently stored. Then, a control device can use the strapping signal to set a substantially permanent mode or state of a device on the chip.
However, systems are increasingly requiring more flexibility during operation. For example, a system may need to temporarily switch modes of the device during a specified time period of operation to change the function of the device for that time period. Conventional systems using the various mode or state setting techniques cannot change the mode or state during operation (i.e., they cannot override the strapping value once it's been stored).
Therefore, what is needed is system than can change a mode or state of a device during operation.